The antineutrino vanishes differently

Researchers report a possible difference between muon neutrino and muon antineutrino disappearance, which if confirmed will have serious implications for our current theoretical understanding.

CPT symmetry, the combination of charge conjugation, parity inversion, and time reversal, is a fundamental symmetry of particle and nuclear physics and is considered sacred. It is conserved in field theories that explain the strong, weak, and electromagnetic interactions. In the lepton sector, CPT symmetry requires that muon neutrino disappearance oscillations be identical to muon antineutrino disappearance oscillations in vacuum. A test of CPT symmetry was recently performed by the MINOS experiment at Fermilab, which, due to its magnetic field, is the first experiment to distinguish μ^- and μ⁺ tracks and separately measure the disappearance of muon neutrinos and muon antineutrinos [1]. (Previous experiments have measured a mixture of neutrino and antineutrino oscillations.) Remarkably, as reported in Physical Review Letters, MINOS appears to observe a difference between muon neutrino and muon antineutrino disappearance [1].